Sift-proof industrial bag



April 1969 H. E KASTING ETAL 3,439,864

SIFT-PROOF INDUSTRIAL BAG Filed Sept. 5, 1967 Sheet 2 of 2 23a 14a 12a23b I l 16a -18a 11a- ;i r 1Ib 23 14b 12b 23d FIG.6.

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INVENTORS HOWARD E. KASTING BEN AMIN @MMNE BY @eir ATTOR United StatesPatent 3,439,864 SIFT-PROOF INDUSTRIAL BAG Howard E. Kasting,Somerville, and Benjamin H. Romaine, North Plainfield, N.J., assignorsto Union Carbide Corporation, a corporation of New York Filed Sept. 5,1967, Ser. No. 665,560 Int. Cl. B65d 33/00 US. Cl. 229-59 7 ClaimsABSTRACT OF THE DISCLOSURE A sift-proof industrial bag having aheat-sealed rectangular-shaped bottom closure formed by a pair ofoverlapping opposed side flaps and a pair of infolded end flaps. Theside flaps and the end flaps are heat sealed directly to each other intheir common areas of overlap. In addition, a portion of the edges ofthe side and end flaps adjacent the corners of the bag are infolded overthe end flaps and heat sealed to the end and side flap.

Field of the invention This invention relates to the production of bagsfrom heat scalable thermoplastic film and more particularly toindustrial type, heavy duty, sift-proof, vented bags suitable forshipping bulk quantities of commodities. Furthermore, this invention isan improvement over the bag of US. 3,220,601, issued Nov. 30, 1965, toH. E. Kasting.

Thermoplastic film of proper thickness has adequate impact, tear andtensile strengths for use as a bag forming material in the constructionof heavy duty bags useful for packaging and shipping bulk quantities ofthe order of 50 to 100 pounds of granular commodities such asfertilizers, molding powders, portland cement, dyes and pigments, andfood stuffs such as sugar, beans, flour and the like. Incontradistinction to the older conventional bag forming material such aswoven fabric or multi-ply paper, a thermoplastic film provides superiorprotection against vermin, accidental wetting of the packaged commodity,loss or gain in moisture content and minimum loss of finely-dividedmaterials by sifting through scams or closures.

Heretofore, thermoplastic film bags have performed well when the productpackaged therein was granular and non-dusting. However, such a bag hasproven to be unsuitable for packaging fine, dusting materials, due tothe small holes found in the corners of the bag. These holes which are afunction of bag construction unfortunately permit leakage offinely-divided material and limit bag product application. Hence, thereis lacking a desirable thermoplastic industrial bag that would permitentrapped air to escape and at the same time would be sift proof forfinely-ground products without any sacrifice to bag strength.

Summary The present invention provides an industrial bag which permitsentrapped air to escape but at the same time is sift proof forfinely-ground products and exhibits high bag strength.

Broadly, the present invention Provides a sift-proof industrial baghaving a heat-sealed rectangular-shaped bottom closure formed by a pairof overlapping opposed side flaps and a pair of infolded end flaps. Theside flaps and the end flaps are heat sealed directly to each other intheir common areas of overlap. In addition thereto, a portion of theedges of the end and side flaps adjacent the corners of the bag areinfolded over the end flaps and heat sealed to the end and side flap.

3,439,864 Patented Apr. 22, 1 969 Description In the drawing:

FIG. 1 is an elevational view of a preferred flattened bag blank cutfrom a length of tubular thermoplastic film and slitted at each end toform a plurality of flaps of a configuration such that the flaps can besealed together in overlapping relationship.

FIG. 2 is a development view of the bottom closure forming portion ofthe open bag blank of FIG. 1 illustrating the fold lines of the end andside flaps.

FIG. 3 is a bottom view of the bag of FIG. 1 after the end flaps and theside flaps have been folded.

FIG. 4 is a bottom view of the bag of FIG. 3 illustrating the heat sealsapplied to form the bottom end closure.

FIG. 5 is an enlarged fragmentary view of the bottom closure of the bagof FIG. 3 illustrating the position of the heat seal in relation to thefolded tuck.

FIG. 6 is an elevational view of a flattened bag blank cut from a lengthof a tubular thermoplastic film and slitted at each end to form aplurality of flaps of a configuration such that the flaps can be sealedtogether in overlapping relationship and which illustrates analternative embodiment of the present invention.

FIG. 7 is a development view of the bottom closure forming portion ofthe open bag blank of FIG. 6 illustrating the fold lines of the end andside flaps.

FIG. 8 is a bottom view of the bag of FIG. 6 after the end and sideflaps have been folded.

FIG. 9 is a bottom view of the bag of FIG. 8 illustrating the heat sealsapplied thereto.

Referring to FIG. 1, a bag blank 10 having longitudinal flattened edges11, 11' are square end cut from a length of heat sealable, flattenedtubular thermoplastic film, as for example, the mono olefin polymerssuch as polyethylene, polypropylene; olefin copolymers such as ethylenepropylene copolymer and ethylene alkyl acrylate copolymers; and vinylpolymers such as rigid and plasticized polyvinyl chloride, polyvinylidene chloride and the like. The tubular film is preferablyseamless tubing such as is formed by the blown tube process as, forexample, by the process described by Fuller in US. Patent No. 2,461,975.The tubular film can also be flat film as formed by slot extrusion orcalendering and thereafter sealed together along its longitudinalmarginal edges to form tubing. If desired, the tubular film can beoriented in various conventional manners to impart improved physicalproperties. Both plies of the flattened tubing 10 are die cut at eachend as shown in FIG. 1 to form a pair of identical bottom formingclosure side flaps 12, 14 (FIG. 2) and a pair of end flaps 16, 18 (FIG.2). Preferably, the die cuts are so made as to provide opposing sideflaps 12, 14 with side edges 13, 15 running diagonally away from theflattened edges 11, 11' and with side edges 13, 15' running parallelaway from the flattened edges 11, 11' whereby the flaps maximum widthdimension lies along the square cut edge 22 being substantiallycoextensive with the width of the flattened bag blank, as for example,about of the bag blank width and the minimum width dimension liesbetween the interior die cut termini 24 and 25. One end of the inwardlydirected sides of side flaps 12, 14 and 12, 14' can be a continuousstraight diagonal cut extending from square cut edge 22 to interiortermini 24, the diagonal being at an angle of about 35 to 55 withrespect to flattened edge 11. Preferably, for ease in manipulation andfolding alignment the die cut is made with a diagonal cut portion 26,26' being at an angle of about 45 with respect to flattened edge 11'.Although each corner of the bag can have this straight diagonal cut itis preferred to provide the other end of side flaps 12, 14 and 12', 14with a continuous straight parallel cut 23, 23' extending from squarecut edge 22 and terminating at one end to a cut portion 27, 27' runningdiagonally from flattened edge 11. This cut is desirable since itprovides a valve opening on both ends of the bag, one of which can beclosed with a final seal. Also this parallel die out can be used in allfour corners of the bag as shown in FIG. 6. Hence, die cuts 23a, 23b,23c and 23d and die cust 25a, 25b, 25c and 25d correspond to die cuts 23and 25, respectively of the bag of FIG. 1. Furthermore, as shown in FIG.7 and flaps 16a, 18a and side flaps 12a, 14a correspond to end flaps 16,18 and side flaps 12, 14 of FIG. 2. However, the resulting configurationis I-shaped when the side flaps are outfolded (FIG. 7).

The film material extending between the cuts in the side flaps 12,14constitutes a tongue portion, these portions being subsequentlyoverlapped and heat sealed together to form a seal resistant in shear toload stress.

The end flaps 16 and 18 as are apparent in FIG. 1, have diagonally andparallel cut side edges complementary to the diagonal and parallel edgesof side flaps 12, 14 and thus are widest at die cut termini 24, 25 andnarrowest at square cut edge 22. Accordingly, as more particularly shownin FIG. 2, each side flap 12, 14 when unfolded along flattened edge 11approximates a square shape diagonally bisected by flattened edge 11.

As shown in FIG. 3 the end flaps 16 and 18 are infolded and the opposedside flaps 12, 14 are then inwardly folded over edges 20 and 21respectively (FIG. 2) in overlapping relationship to each other and withrespect to flattened end flaps 16, 18. The necessary equipment suitablefor carrying out this folding operation is fully described in US.3,220,601 referred to hereinabove, as well as the heat sealingapplication. In the alternative impulse sealing of the folded flaps canbe used to form the final seals.

Referring to FIGS. 4 and the heat sealing together of the end flaps andside flaps to form a sift proof yet ventable bottom closure isaccomplished by fusing together all overlapping film plies. Hence, theresulting bottom closure assumes a substantially flat rectangular shapeupon the bag being filled with a pourable commodity.

Hence, a sift-proof industrial bag which is ventable is obtained byoverlapping the opposed side flaps 12, 14 and infolding the end flaps16, 18. In addition thereto, the side flaps 12, 14 and the end flaps 16,18 are heat sealed directly to each other in their common areas ofoverlap (FIGS. 3, 5). Furthermore, as shown in FIGS. 3 and 5, a portionof the edges 16', 18' of the end flaps 16, 18 and a portion of the edges12, 14' of the side flaps 12, 14 adjacent the corners of the bag areinfolded over the end flaps producing a triangular tuck 30 with inwardedges at the corner of the bag and heat sealed 28 to the end and sideflap. The heat seal 28 is made extending almost to the apex of the tuck30. Alternatively, if the die cuts of FIG. 6 is employed, the bag endwhen folded assumes the configuration of FIG. 8 with tucks 30a in allfour corners as shown. These tucks, likewise, are formed when a portionof the edges of the side and end flaps adjacent the corners of the bagare infolded over the end flaps and heat sealed to the end and sideflap. A heat seal pattern as shown in FIG. 9 is suitable for such a bagconfiguration although not limited thereto.

The above design in combination with the heat seal forms a labyrinthtype passageway which allows air to escape, but retains bag ingredientsor particles. A secondary benefit of this cut and fold is the improvedstrength of the seal at the point where the side flap seals stop on theend tabs 32. In the preferred form of the invention the straight anglecut and the closure seal are both made on a 45 angle with the flat edgeof the bag. The location of the seal is such as to bisect the angle ofthe tuck 30.

The top closure for the bag can be made in various ways including heatsealing together the opposing walls, stapling or clamping with metalfasteners, sewing, tying with twine, or knotting the gathered end.Preferably however, the bag is a rectangular top closure similar to thebottom closure, the closure being provided with a filling valve forreadily filling the bag with a pourable commodity, the valve beingcloseable by pressure being exerted thereon by the filling bags contentscausing the valve walls to collapse against each other.

The bag of the invention was subjected to various drop test andstructural tests as set forth in US. 3,220,601 and were found to have amuch lower incidence of breakage than conventional multi-ply paper bagsand bags made of thermoplastic film heat sealed together by pinched typeseals or face to face seals. Furthermore, the bag was found to be siftproof as well as ventable.

The superior resistance to breakage of the thermoplastic film bags ofthis invention, particularly in the area of the bottom and top closuresis a direct result of the closures having been formed by sealingtogether in overlapping relationship the several flaps constituting theclosure whereby the stresses transmitted to the bag walls by itscontents are resisted in shear. Further contributing to the bagsresistance to breakage is the double and triple film ply construction ofthe bags several corners which are formed by the sealed overlap of theside flaps and each end fiap.

Although this invention has been described in a particular detail withrespect to bags made from plastic film of a single wall thickness, theprinciples of this invention are applicable to the manufacture of bagsfrom laminated thermoplastic films including such composite films aslaminates of polyethylene film and polypropylene film, a polyethylenefilm and vinylidene chloride polymer or copolymer; of plasticized vinylchloride polymer or copolymer film and polyethylene film; ofpolyethylene film and regenerated cellulose film coated with a heatsealable coating; of a heat sealable thermoplastic film such aspolyethylene film or plasticized vinyl chloride polymer or copolymerfilm in a metal foil such as aluminum foil; of thermoplastic films suchas polyethylene and a fibrous web such as paper woven or unwoven fabricsof organic or inorganic fibers such as cotton fibers, rayon fibers,nylon fibers, linear polyester fibers, polyacrylonitrile fibers,asbestos fibers and glass fibers.

In the use of such laminated films, it is preferred, that both outerlaminate surfaces be a heat sealable thermoplastic material in order toobtain strong shear-resistant seals in the bags bottom and top closures.

By suitable choice of the various materials in a film laminate it ispossible to provide desired vapor transmission rate through the bagwalls, resistance to attack by corrosive packaged commodity, heatresistance, abrasion and scutf resistance, opacity to light,particularly in the instance of metal foil, and improved flexural,impact and tensile strengths as, for example, in the instance oflaminates having a reinforcing fabric ply.

Bags can also be made according to this invention from a plurality ofconcentrically assembled individual tubular films of substantially thesame flat width, such films being of the same or different polymers.Bags made of such multi-ply films generally offer such advantages asimproved energy absorbing characteristics, and puncture and abrasionresistance over bags made of single ply films of the same thickness asthe multi-ply film thickness.

It will be readily apparent to those skilled in the art that variouschanges and modifications can be made in the above description of theinvention without departing from the nature or spirit thereof. Thus, forexample, it is feasible, if desired, to substitute for the seamlesstubular film from which the bag blank was die cut, tubing made bylongitudinally edge sealing a fiat sheet of thermoplastic film.Moreover, instead of heat sealing the overlapped plies to form sealsresistant to shear to applied stress it is within the contemplation ofthe invention to use other methods of sealing as, for example,adhesives, or solvent seals which are usually more expensive in time andmaterial cost than the aforedescribed heat seals.

What is claimed is:

1. In a thermoplastic film bag having a heat-sealed rectangular-shapedbottom closure formed by a pair of overlapping oppose'd side flaps and apair of infolded end flaps, said side flaps and said end flaps beingheat sealed directly to each other in their common areas of overlap, theimprovement which comprises a sift-proof, industrial bag wherein aportion of the edges of the side and end flaps adjacent the corners ofthe bag are infolded over the end flaps and heat sealed to the end andside flap to form at least one sift-proof air vent pocket.

2. A sift-proof bag according to claim 1 wherein the film ispolyethylene film.

3. A sift-proof bag according to claim 1 wherein at least one pair ofside edges of said side flaps and said end flaps are tapered.

4. A sift-proof bag according to claim 1 wherein said side flaps eachhave an inwardly tapering terminal edge and side edges runningperpendicular to the bag length, and said end flaps each have interioredges of a configuration complementary to said side flap edges.

5. The sift-proof bag of claim 1 wherein the side and end flaps adjacentthe valve end of the bag are infolded and heat sealed together to format least one sift-proof air vent pocket at the valve end of the bag.

6. The sift-proof bag of claim 5 wherein both side flaps are partiallytapered at the valve end of the bag.

7. The sift-proof bag of claim 5 wherein both side flaps are cutdiagonally with respect to their respective hinge lines along theinitial portion of their opposed side edges where said edges extend fromthe bag at the valve end thereof, each such side edge then being cutperpendicular to the hinge line of each flap.

References Cited UNITED STATES PATENTS 3,220,601 11/1965 Kasting229-62.5 3,220,635 11/1965 Kasting et a1 22962.5 X 3,220,636 11/1965Kasting 22957 3,248,042 4/1966 Kasting et al. 22959 X 3,343,748 9/196-7Calvert 229-59 DAVID M. BOCKENEK, Primary Examiner.

US. Cl. X.'R. 22957, 62.5

